Back in February it was a cop killer named Christopher Dornan who had law enforcement families across Southern California. Double locking their doors we'll tonight officers of the court and their loved ones in taxes. Know that feeling of vulnerability after the murder of a district attorney and his wife and an assistant DA. Proof that taking the oath to keep the peace comes with a price at ABC's Pierre Thomas has the latest on the manhunt. The PM will receive -- call. All that seriously hurt veteran district attorney gunned down in his own home alongside his wife this weekends -- -- -- Did vanity. There's very much -- killing wife Cynthia. -- to. -- -- -- -- -- Kaufman county district attorney Mike McClellan apparently executed by multiple shots from an assault rifle. His wife Cynthia murdered two as the assailants forced his way in. Such a brazen attack on the top law enforcement official is almost unheard of in small communities like this one. But just weeks ago Mike McClellan himself stood before -- bank of microphones. And spoke directly to the unknown killers of one of his top deputies. Assistant DA mark -- was shot in broad daylight. Outside the county courthouse in January. By two suspects -- -- blacks what year. I hope that. The people lived in this or watching. Because. We're very confident that. We're gonna find you. -- -- -- -- -- -- -- -- But instead of tracking down those killers -- -- was gunned down as well. This is the third killing of a public safety official in weeks and -- of shock wave of fear and a nationwide search for answers. Obviously were an attack we've seen. Two attacks within the last few months and dish attorneys and they even have a law enforcement officials there's certain vulnerability there's no doubt about it. Would be less than honest -- quote was not -- Security county buildings and even at the -- -- has been visibly increased we're very much on the lower. We obviously have some -- that are out -- -- -- to. Elected officials. And so we take -- -- seriously the bold attacks have spurred a warning from the national district attorneys association. The truth of the matter is if somebody wants to kill you. As a prosecutor. It's very difficult. To deal with that because we don't have security details so what. -- prosecutors telling each other and their staffs across the state. The first thing they -- this morning when they open their offices is reevaluating their security. Every office I think at this point is concerned about that and they're talking to local law enforcement and their own investigators about. What they need to be doing to protect themselves. But who would do such a thing. Officials tell ABC news they have -- good leads to county sheriff's department is taking the lead in the case. But dozens of investigators from the Texas Rangers the FB IA TF and the US marshals have joined the hunt. Prosecutors are reviewing cases looking for motives. And any similarities in the cases including any possible links to the murder of Colorado's -- of corrections. Gunned down -- his front door just two weeks ago. -- -- -- The suspect in that case -- evil was believed to be a member of a white supremacist prison gang. Who led Colorado and was killed in a high speed chase just 100 miles from Kaufman county. He came about me he was sick and about a hundred miles an hour before his death McClellan said his office had made a big dent into the white supremacist group. Aryan brotherhood of Texas and just last -- federal prosecutors indicted dozens of members of the group. On multiple charges of drug trafficking. Sources tell ABC news last December law enforcement officials sit out a bulletin warning that the group planned to retaliate. Certainly if it turns that's been the case there would approve the aryan brotherhood of Texas was involved in these -- it's very cartel like these games -- can -- capable of extreme violence against her own members against rivals. And you know maybe they've decided to part of public officials were standing in the way of their business. A clear. Concern to individuals who are in public life particularly those who deal with some very. Mean and vicious individuals whether -- white supremacy groups or whether there. The of the drug cartels that we have whatever the motive behind the attacks in Kaufman the ramifications. Are clear. It's not only an assault on those two and their families. But it's an assault on the rule of law it's an assault on the criminal justice system and we've got to find them and find and quickly. Tonight the streak with a grisly murders took place has reopened. But still there are uneasy feelings especially among the people whose job it is to defend us now feeling under assault. For Nightline on Pierre Thomas -- Texas.

This transcript has been automatically generated and may not be 100% accurate.

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